1. Field Of The Invention
This invention relates to packaging utilizing a wrapping machine wherein a wrapping sheet is formed into a tube for wrapping product therein and more particularly to a self threader for the wrapping sheet.
2. Background Of The Invention
Over the past several decades, various types of wrapping machines have been developed for wrapping products articles. One type of wrapping machines includes shrink wrap packing machines. Shrink wrap packaging has become widely used to provide a low cost packaging technique for a wide assortment of articles. Typically, the article or articles are incased within a wrapping sheet and is passed through a heating oven whereby the wrapping sheet incases the article or articles by the contraction of the wrapping sheet. Although, the use of shrink wrapping techniques is simple in theory, the physical wrapping of the article or articles by the wrapping sheet encounters some difficulties depending on the shape and number of articles to be encased within the wrapping sheet. Since the typical shrink wrap packaging machine operates at high speed, the handling of the wrapping sheet presents a complex engineering problem for the shrink wrapping pachaging machine. In addition, any defective wrap and/or tearing of the wrapping sheet will produce defective packages thereby requiring the wrapping process to be terminated and requiring the wrapping sheet to be re-threaded and/or adjusted within the wrapping machine. Such a termination of the wrapping process is significantly costly as well as requiring an operator to re-adjust and/or re-thread the wrapping sheet within the machine. Typically, the wrapping sheet is disposed proximate to a heating oven thereby increasing the danger of burning or the like by the operator.
One specific type of shrink wrapping machine incorporates a tube former commonly referred to as a forming shoe for forming a wrapping sheet of heat shrinkable material into a longitudinally extending tube. The tube is sealed on terminating end and by a seal bar with a first and second edge of the wrapping sheet being in an overlapping relationship and secured to one another by electrostatic adhesive or welding means. The forming tool includes a first forming plate and a second forming plate for forming the wrapping sheet within the tube with the first and second edges disposed in the overlapping relationship.
Although the use of a first and second forming plate has provided a suitable means for forming the longitudinal extending tube of the wrapping sheet, this prior art tube former has certain disadvantages. Firstly, the wrapping sheet must be hand threaded between the first and second forming plates by an operator. Secondly, the prior art forming tools lack any positive means for maintaining the position of the first edge of the wrapping sheet between the first and second forming plates. The tension of the sheet was relied on to maintain the position of the first edge of the wrapping sheet within the first and second forming tool plates.
Therefore, it is an object of this invention to overcome these disadvantages of the prior art wrapping machine and provide a self threader for a wrapping machine for self threading a wrapping sheet within a tube former.
Another object of this invention is to provide a self threader for a wrapping machine which provides a positive means for maintaining the position of the wrapping sheet within the tube former.
Another object of this invention is to provide a self threader for a wrapping machine which is both simple and effective without appreciably raising the cost of the wrapping machine.
Another object of this invention is to provide a self threader for a wrapping machine which may be easily adapted to existing wrapping machines.
The foregoing has outlined some of the more pertinent objects of the present invention. These objects should be construed as being merely illustrative of some of the more prominent features and applications of the invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or modifying the invention with in the scope of the invention. Accordingly other objects in a full understanding of the invention may be had by referring to the summary of the invention, the detailed description describing the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.